How do I calculate Vc and i for an RC circuit with a closed switch?

In summary, the conversation discusses a circuit with a switch that has been opened for a long time and then closes at t=0. The problem involves two voltage sources and the calculation of Vc(t) and i(t) for t>0. The student is unsure about their approach and asks for tips and help. The expert advises to consider the voltage drop in the 2K resistor and the charging or discharging of the capacitor through a resistor.
  • #1
CursedAntagonis
23
0

Homework Statement


The switch in the following circuit has been opened for a very long time and then closes at t=0 (a) Calculate Vc(t) for t>0. (b) Calculate i(t) for t>0.

Homework Equations





The Attempt at a Solution


circuits1.jpg


Here is my attempt of the problem. I have not dealt with a problem that has two voltage sources before. Also, I have not dealt with a problem that does not become source free after the switch is either opened or closed. I am not sure if I am on the right track, I have getting Vc for t<0 to be 24V, however, Vc for t>0 is 36V?... I thought the Vc for both t>0 and t<0 stays the same. Any tips and help is greatly appreciated.
 
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  • #2
Before you close the switch, there are 3 series resistors with 36 volts at one end and 12 volts at the other.
You have worked out the current, but you need to work out the voltage across the capacitor as this will change when you close the switch.

(Work out the voltage drop in the 2K and subtract it from 36 volts).

The capacitor will discharge or charge depending on the new voltage distribution when you close the switch, so you have to allow for the way that capacitors charge or discharge through a resistor.
 

Related to How do I calculate Vc and i for an RC circuit with a closed switch?

1. What is an RC circuit?

An RC circuit is a type of electrical circuit that consists of a resistor (R) and a capacitor (C) connected in series or parallel. It is commonly used for filtering, smoothing, and time-delay applications in electronic circuits.

2. How does an RC circuit work?

An RC circuit works by storing electrical energy in the capacitor and releasing it through the resistor. As the capacitor charges and discharges, it creates a time-varying voltage across the circuit. The resistor controls the rate at which the capacitor charges and discharges, affecting the behavior of the circuit.

3. What is the time constant of an RC circuit?

The time constant of an RC circuit is a measure of how quickly the capacitor charges or discharges. It is calculated by multiplying the resistance (R) in ohms by the capacitance (C) in farads. The time constant is typically denoted by the symbol τ (tau) and has units of seconds.

4. How do you analyze an RC circuit?

To analyze an RC circuit, you can use Kirchhoff's laws and Ohm's law to calculate the voltage, current, and power at different points in the circuit. You can also use differential equations to model the behavior of the circuit over time. There are also various circuit analysis techniques, such as Thevenin's theorem and nodal analysis, that can be used to simplify and solve complex RC circuits.

5. What are some real-world applications of RC circuits?

RC circuits have a wide range of practical applications, including in filters for audio and radio signals, in power supplies for electronic devices, and in timing circuits for electronic clocks and watches. They are also commonly used in electronic devices to smooth and stabilize voltage levels and as part of oscillators and time-delay circuits in electronic systems.

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